Visualization of horizontally-aligned single-walled carbon nanotube growth with¹³C/¹²C isotopes

Horizontally aligned growth of single-walled carbon nanotubes (SWNTs) on single-crystal surfaces has attracted great interest in terms of nanoelectronic applications, but their growth mechanism is not fully understood. We report on the ¹³C/¹²C isotope-labeled growth of SWNTs on a sapphire surface to visualize their growth process. Switching carbon feedstock from ¹³CH₄ to ¹²CH₄ during SWNT growth induces a gradient distribution of the carbon isotopes along the tube axis. From the Raman mapping analysis, we succeeded to observe the gradual change in the isotope distribution of individual SWNTs. The results indicate the base-growth mode for the horizontally aligned SWNTs, which suggests that nanotube-sapphire interaction is essential to alignment. This method offers a unique technique to analyze the nanotube growth mechanism and kinetics.